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answered already you need to find out cubic feet needed for one en closer that can handle one of your subs,.they give you the measurements when you find one on line that one sub fits. multiply that figure by 4 and that should give you what you need for total space needed and split that four ways with the stock your using to build box then you will have the right size en closer for each sub.at least its something to go by.if your going to vent it see what size vent that one en closer has in it and times that figure by 4 and that should put you in the ball park for a vent size or if you split each sub in its own en closer just put 4 different vents one for each sub.good luck

2011 Silverado Extended Cab Subwoofer Box

Doesn't it have a sub under neath the Center console?

I have a 2007 2500HD silverado ltz and there is a sub under the center console.